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FAQ 004780 | I would like to perform a stability analysis of the upper flange in a long truss. What is the best way to proceed?
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I would like to perform a stability analysis of the upper flange in a long truss. What is the best way to proceed?Answer
According to DIN EN 1993‑1‑1:2010‑12 [1], Annex BB.1.1, the buckling length may be used in the individual bracing under certain conditions. This means that in this case, the individual members, not a set of members, can be applied with the effective length factors specified in the standard.
Since this approach only considers the local failure, it is necessary to analyze the global failure of the entire structure. For this design, the set of members must have the corresponding imperfection. Under certain conditions, the design can be performed on single members, depending on the model (for example, a tower), or the set of members must be analyzed for a failure from the plane (the truss), as in the attached example.
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Dlubal FAQ Truss Bracing Stability Equivalent member Effective length Frequently Asked Question FAQ about Dlubal Question and Answer about Dlubal
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![[EN] KB 001670 | Design of a welded truss](/-/media/Images/netgenium/thumbnails/2/9/6/7/4/2967457/2967457.png?la=en-US&mw=348&mlid=A590711DE2704786B5F8D1A306AF82E8&hash=70A835C75F046923B114D0BE66F68A215563B70E)
![[CS] Assessment of cold formed steel sections according to Eurocode 3](/-/media/Images/netgenium/thumbnails/2/4/5/9/2/2459200.png?la=en-US&mw=348&mlid=7CF9488DF3FD44B2A237A71364421BA2&hash=3DABE499C39AF3CD3339581552C6CB574484EB38)
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Manual adjustment of the buckling curve according to EN 1993-1-1
The RF-/STEEL EC3 add-on module automatically transfers the buckling line to be used for the flexural buckling analysis for a cross-section from the cross-section properties. In particular for general cross -sections, but also for special cases, the assignment of the buckling line can be adjusted manually in the module input.
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Calculation of warping springs for consideration in the lateral -torsional buckling analysis for open cross -sections
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Determination of Effective Widths According to EN 1993-1-5, Annex E
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Automatically ignore curved c/t-parts when classifying cross-sections
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Consideration of the net cross-section for tensile stress according to EN 1993-1-1
SHAPE-THIN | Cold-Formed Sections
SHAPE-THIN determines the effective cross-sections according to EN 1993-1-3 and EN 1993-1-5 for cold-formed sections. You can optionally check the geometric conditions for the applicability of the standard specified in EN 1993‑1‑3, Section 5.2.
The effects of local plate buckling are considered according to the method of reduced widths and the possible buckling of stiffeners (instability) is considered for stiffened sections according to EN 1993-1-3, Section 5.5.
As an option, you can perform an iterative calculation to optimize the effective cross-section.
You can display the effective cross-sections graphically.
Read more about designing cold-formed sections with SHAPE-THIN and RF-/STEEL Cold-Formed Sections in this technical article: Design of a Thin-Walled, Cold-Formed C-Section According to EN 1993-1-3.
- I would like to perform a stability analysis of the upper flange in a long truss. What is the best way to proceed?
- I perform a stability analysis of a beam for lateral-torsional buckling. Why is the modified reduction factor χLT,mod used in the design according to DIN EN 1993‑1‑1, 6.3.3 Method 2? Is it possible to deactivate this?
- I need to define different types of lateral intermediate restrains for a single element in RF-/STEEL EC3. Is this possible?
- I compare the flexural buckling design according to the equivalent member method and the internal forces according to the linear static analysis with the stress calculation according to the second-order analysis including imperfections. The differences are very large. What is the reason?
- Why are the equivalent member designs grayed out in the Stability tab when activating the plastic designs by using the partial internal force method (RF‑/STEEL Plasticity)?
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I design a set of members by using the equivalent member method in RF‑/STEEL EC3, but the calculation fails. The system is unstable, delivering the message "Non-designable - ER055) Zero value of the critical moment on the segment."
What could be the reason? - I cannot see any members if the RF-/STEEL EC3 add-on module is selected as a "load case," why?
- To which axes refer the support rotations and support eccentricities in RF‑/STEEL EC3 Warping Torsion?
- What does the load application point in RF-/STEEL EC3 Warping Torsion refer to?
- Why do I get different design results for a load combination (CO) and a result combination (RC) in STEEL EC3 in spite of the same internal forces?
